Re: [PATCH v2 2/2] x86: don't unmask disabled irqs when migrating them

[Jeremy Fitzhardinge <jeremy@goop.org>]

On 05/09/2011 10:44 AM, Tian, Kevin wrote:
>> It doesn't really need to be an irq.  The main reason was so that it would
>> appear in /proc/interrupts so I could use the counter as a "number of times a
>> spinlock was kicked" counter.  That could be exposed in some other way if
>> being part of the interrupt infrastructure brings too much baggage with it.
>>
> Perhaps we don't need an irq binding here. Just like a local APIC interrupt
> source which only needs vector. Somehow the virq or vipi concept in Xen
> context is similar.

An event channel is logically equivalent to a vector, so that would make
sense.  We currently allocate irqs for cross-cpu call and reschedule
event channels, whereas native x86 simply uses a naked vector for
those.  But they are real interrupts, so an irq at least makes some
logical sense in those cases.

For spinlocks, the event channel is more like a usermode-level signal
which is always blocked and only ever tested with sigsuspend (or is it
sigpoll?  something like that).

    J